It has long been recognized that elastic fibers play an important functional role in aorta and large blood vessels. Elastic fibers can be divided both morphologically and chemically into two distinct protein components referred to as elastin and microfibril. During the formation of elastic fibers, ultrastructural data reveals that the microfibril is deposited first in the extracellular matrix and appears to act as a framework upon which elastin is oriented and insolubilized. The objectives of this proposal are to chemically define the microfibril protein and its rate of synthesis in both normal and abnormal elastic fiber formation. Studies will involve: (1) chemical characterization of the microfibril, (2) production of monoclonal antibody to the microfibril with subsequent use of the antibody to localize the microfibril at the electron microscopic level, (3) isolation and cell-free translation of microfibril mRNA including examination of the possible existence of a leader sequence (4) examination of the amount of functional microfibril mRNA and rate of microfibril synthesis during chick aorta embryonic development, and (5) examination of the amount of functional microfibril and elastin mRNAs and their rate of synthesis during the induction of hypercholesterolemia in chicks. Hopefully these studies will provide insight into the normal course of elastic fiber formation as well as providing insight into an abnormal situation in which an operative repair mechanism for elastic fibers is lacking.